The research brings us a step closer to early diagnosis of the more common type Alzheimer's that produces symptoms after age 60.

Washington University neurologist Dr. Randall Bateman says researchers saw changes in the brain scans, spinal fluid, and blood of people with inherited Alzheimer's as much as 15 to 20 years before the onset of symptoms.

Bateman says the next step is a clinical trial for those with the early-onset, inherited form of the disease.

"The prediction is that, if we use the right drugs in the right amount, and at the right stage of the disease in the patient, that we would be able to prevent or delay the onset of Alzheimer's disease in these individuals," Bateman said.

Bateman says the hope is that the same biological markers can eventually be used to diagnose the much more common form of Alzheimer's that develops later in life.

"If someone had a positive scan at age 60 could we say when they would develop dementia or even that they inevitably will develop dementia? We can't say that at this point," Morris said. "And plus, we have very little that we can do to modify the course, whatever the course is going to be."

Morris says for now, the next step is to try to prevent or delay the debilitating symptoms of Alzheimer's in people with the rare, early-onset form of the disease.